Tube rack



FIG. 1 is a perspective view of a tube rack showing my new design;

FIG. 2 is a side elevational view of the tube rack;

FIG. 3 is an end elevational view of the tube rack;

FIG. 4 is a top plan view of the tube rack;

FIG. 5 is a bottom plan view of the tube rack; and

FIG. 6 is a fragmented cross-sectional view taken along line 6--6 of FIG. 1. 

The ornamental design for a tube rack, substantially as shown and described. 